Method of anchoring an anchoring bolt in a bore hole

ABSTRACT

A method of anchoring an anchor bolt in a bore hole in which a fast-setting agent and cement mortar are introduced into the bore hole, which comprises the steps of filling the bore hole completely with cement mortar and introducing simultaneously with the cement mortar a container of a fast-setting agent in the end of said bore hole, and crushing the vessel by the insertion of an anchor bolt.

Gruber July 1, 1975 METHOD OF ANCHORING AN 2,952,129 9/1960 Dempsey .1 61/45 B I B LT [N B RE HOLE 3,283,513 ll/l966 kierans et al.... X ANCHOR NC A 0 3,324,662 6/1967 McLean v. X [75] Inventor: Rudolf Gru r, K rm Austria 3,541,797 11 1970 Stewart 61/45 B x Assigneez GD Anker Gebirgs Duebe| Anker 3,6l8,326 ll/l971 Montgomery 61/45 B GmbH 84 Co. KG, Karnten, Austria FOREIGN PATENTS OR APPLICATIONS J 25, Austria t v t B PP 373,189 Primary ExaminerDennis L. Taylor Attorney, Agent, or FirmErnest G. Montague; Karl [30] Foreign Application Priority Data ROSS; Herbm't Dubno J 26, I972 A O 47 72 une ustrla O 3/ [57] ABSTRACT [52] us. Cl 61/45 B A methvd 0f anchoring n n h r olt in a bore hole [5]] Int. Cl. E21d /00 in which a fast-Setting agent and Cement mortar are [58] Fi ld of S h M 61/45 B R, 63; 52/693 introduced into the bore hole, which comprises the 52/704; 106/106, 89, Steps of filling the bore hole completely with cement mortar and introducing simultaneously with the ee- [56] Refer n Cit d ment mortar a container of a fast-setting agent in the end Of said bore hole, and crushing the vessel the 2,849,866 9/1953 Flygare et a1 u 61 /45 B memo of an anchor bolt 2,930.]99 3/1960 .larund 6l/45 B 1 Claim, 2 Drawing Figures METHOD OF ANCHORING AN ANCHORINGBQLT IN A BORE HOLE The present invention relates to a method of anchoring an anchor bolt in a bore hole, in which a rapidbonding agent and cement mortar are introduced into the bore hole.

Such anchor bolts are used primarily in the construction of tunnels or galleries, but they are also used in above-ground construction. In gallery construction they have the object of preventing the falling of rock, in place of temporary timbering, until the final walling of the tunnel or gallery.

correspondingly long blind holes are drilled in the roof or walls of the galleries or tunnels, depending on the nature of the rock, and cement mortar is forced into these holes by compressed air or pumps using a hose, the hose being inserted into the bore hole up to the end thereof and being gradually withdrawn as the bore hole becomes filled. Thereupon the anchor bolts, which are made of profiled steel, for instance twistedrib steel, are driven in. Anchor plates are placed over the ends of the bolts which extend out of the bore holes and are pressed by nuts against the rock, the projecting nuts being screwed onto threads provided on the ends of the bolts. Such anchor bolts are referred to as nonpre-stressed anchors. However, increasing in popularity are pre-stressed anchor bolts whose heads are anchored in the bore holes, so that they can be stressed by tightening the nuts which rest against the anchor plates.

Such a stressing of the anchor bolts should take place rapidly. particularly in friable rock. Therefore, the cement mortar used for the anchoring of the bolt heads must set within a short time, for which purpose quicksetting additives must be introduced into the cement mortar.

It has also been proposed first of all to introduce a quick-hardening cement mortar into the bore hole over a length of 50 to 100 cm and then fill the remaining part of the hole with a normally setting cement mortar and drive the anchor bolts in. After the hardening of the rapid-hardening cement mortar, the anchor bolt can be pre-stressed, while the setting of the normal setting mortar takes place a few hours later. This technique was, however, not able to gain general acceptance, since the accurate mixing of the rapid-setting mortar on the spot was difficult, and because this mortar hardened already in part in the pouring apparatus and in the hose; furthermore, the second pouring device required for the normally setting mortar made the work cumbersome. In addition, the anchor bolt had to be driven immediately into every bore hole which had been filled in this manner, so that continuous, economic anchoring of the bolts was not possible.

It is also known to insert a perforated sleeve filled with a fluid cement mortar into the pre-drilled hole by means of an anchor bolt and, after the sleeve has reached the end of the bore hole, drive the anchor bolt into the sleeve. The anchor bolt as it penetrates into the sleeve presses the cement mortar through the perforations of the sleeve and into the bore hole.

Although the sleeve makes possible the use of cement mortar of low water content, the setting time of the mortar is nevertheless so long that the anchor can be subjected to load only 8 to 10 hours later. Prestressing of the anchor bolt is not possible with this manner of operation.

There is also known a method of fastening anchors in bore holes by a chamberized cartridge for the sealing composition, which cartridge is introduced into the bottom of the bore hole. The one chamber of the easily destroyed cartridge contains, for instance, a synthetic resin with accelerator, and the other a hardner. The cartridge is destroyed by the anchor as it is pushed in. The mixing of the composition which fills up only the end of the bore hole is effected by the rotary introduction of the anchor shank which is formed as a mixing screw at its end. A useful sealing composition is obtained only with intensive rotation of the anchor which has been driven in and which produces thorough mixing as a result of its shape. With the length of anchor bolts of up to 12 m used in modern mining, it is understandable that the turning of the anchor is lo longer possible. Furthermore, the sealing only of the anchor head has the disadvantage that the free shank and therefore the predominant part of the anchor does not possess any holding function.

It is one object of the present invention to avoid the disadvantages of the known methods. The invention is with cement mortar and at the same time with the rapid-setting agent in a container is deposited in the bottom of the bore hole, the vessel being destroyed in known manner by the pushing in of the anchor bolt.

The method of the invention makes it possible to use a single type of mortar and furthermore a normal setting cement mortar which can be worked for a long time. Therefore, a large number of bore holes can be filled with the mortar one after the other since there is no danger of early hardening as long as the container containing the fast-setting addition has not been destroyed. The anchor bolts are thus driven one after the other into the bore holes.

In this way, a time-saving manner of operation, simple preparation of mortar and simple maintenance and cleaning of the pouring devices and hoses is possible. Upon the crushing of the container by the anchor bolt, the fast-setting additive passes through the cement mortar which rapidly sets in the vicinity of the head end of the bolt, so that the bolt can be stressed a short time after it has been driven in. The setting time can be substantially controlled by the selection of the chemical composition of different fast-setting agents.

As already mentioned, the cement mortar is introduced into the bore hole througha hose under the action of pressure. In accordance with the present invention, the container can be driven into the bore hole by the cement mortar which is injected under pressure.

For this insertion, the container is made cylindrical and its outside diameter is somewhat smaller than the inside diameter of the injection hose. It is pushed into the free end of the mortar hose and brought with the latter into the end of the bore hole. The mortar forced into the hose presses the container out of the hose and embeds it during the further filling of the bore hole. The vessel may be made of glass or any other material which can be readily be destroyed by the anchor bolt.

In accordance with another feature of the preseent invention, the container, in addition to having the fastsetting addition also contains balls of ceramic, plastic or the like or fine stone chips as rigid displacement members. As soon as the glass vessel has been crushed by the anchor bolt which preferably has a conical end,

the rapid-setting addition wets the mortar, the mixing being promoted by the displacement and shifting of the mortar effected by the anchor and the balls. The material of which the balls is made is of no importance, but it is advisable for the balls to be hard and resistant. The anchor bolt is then wedged against the bore hole wall by the balls, as a result of which its anchoring is further increased. The driving in of the anchor bolt is not impaired by the balls, since they can roll away between the anchor and the wall of the bore hole if, in accordance with another feature of the invention, the diameter of the balls corresponds at most to the difference between the radius of the bore hole and the radius of the anchor head.

The size of the balls therefore depends on the diameter of the bore hole.

One embodiment of the ancor support in accordance with the invention is shown in the drawing, in which FIG. 1 is a cross section through a bore hole just before the driving in of the anchor, and

FIG. 2 is a section through a fastened anchor.

The vessel 3 is introduced into the bore hole 1 at the same time as the introduction of the cement mortar 2. The vessel is located at the bottom of the bore hole and contains, in addition to the fast-binding agent 4, also balls 5 which, upon the driving in of the anchor 6, serve for the mixing of cement mortar 2 and fast-setting agent 4. If the anchor 6 is now driven into the bore bole, shortly before reaching its end position, it will crush the vessel 3, the fast-setting agent 4 will emerge and, due to the good mixing effected by the balls 5 which are displaced by the anchor bolt, will become effective very rapidly.

FIG. 2 shows the fastened anchor in cross section. In the vicinity of the head of the anchor there is located the rapidly solidified zone of the fast-setting 7, the balls 5 assuring additional holding power. Adjoining this is the region of the normal mortar mixture 2. It is essential for this region of the anchor and bore hole to be filled completely, since only then is there obtained a retaining force (lines of force 8) on the rock over the entire length of the pre-stressed anchor. For the stressing of the anchor, an anchor plate 9 and a nut l. on the threaded shank of the anchor bolt are used, in known manner.

I claim:

1. A method of anchoring an anchor bolt having a pointed end in a bore hole having a bottom, comprising the steps of:

a. filling a container of a frangible material with balls having a diameter at most equal to the difference between the radius of said bore hole and the radius of said bolt and with an agent capable of reacting with mortar to accelerate the hardening thereof;

b. fitting a container into an end of a hose;

c. inserting said hose into said bore hole substantially to the bottom thereof;

d. forcing cement mortar activatable by said agent through said hose to drive said container out of the end of said hose against the bottom of said bore hole;

e. gradually withdrawing said hose while continuing to force cement mortar therefrom, thereby completing filling the bore hole ahead of said container with said cement mortar; and

f. driving said bolt into said bore hole through the cement mortar ahead of said container and into said container to rupture same and release said agent for reaction with said mortar and simultaneously release said balls, said pointed end of said bolt wedging said balls against the wall of said bore hole. 

1. A method of anchoring an anchor bolt having a pointed end in a bore hole having a bottom, comprising the steps of: a. filling a container of a frangible material with balls having a diameter at most equal to the difference between the radius of said bore hole and the radius of said bolt and with an agent capable of reacting with mortar to accelerate the hardening thereof; b. fitting a container into an end of a hose; c. inserting said hose into said bore hole substantially to the bottom thereof; d. forcing cement mortar activatable by said agent through said hose to drive said container out of the end of said hose against the bottom of said bore hole; e. gradually withdrawing said hose while continuing to force cement mortar therefrom, thereby completing filling the bore hole ahead of said container with said cement mortar; and f. driving said bolt into said bore hole through the cement mortar ahead of said container and into said container to rupture same and release said agent for reaction with said mortar and simultaneously release said balls, said pointed end of said bolt wedging said balls against the wall of said bore hole. 